Persistent compressed expiring dict in Python, backed up by sqlite3 and pickle, with auto-cleaning and auto-vacuuming semantics
A lightweight wrapper around Python’s sqlite3 database with a simple, Pythonic dict-like interface. This fork is modified to implement a metatable and automatic expiring and vacuuming semantics, as well as some appropriate locking. This also compresses values automatically.
>>> from expiringsqlitedict import SqliteDict >>> with SqliteDict('./my_db.sqlite', autocommit=True) as mydict: >>> mydict['some_key'] = any_picklable_object >>> print mydict['some_key'] # prints the new value >>> for key, value in mydict.iteritems(): >>> print key, value >>> print len(mydict) # etc... all dict functions work
Pickle is used internally to (de)serialize the values. Keys are arbitrary strings, values arbitrary pickle-able objects. This must be used within a context manager.
Values can be any picklable objects (uses cPickle with the highest protocol).
Support for access from multiple programs or threads, using a lockfile.
Support for custom serialization or compression:
# use JSON instead of pickle >>> import json >>> mydict = SqliteDict('./my_db.sqlite', encode=json.dumps, decode=json.loads) # apply zlib compression after pickling >>> import zlib, pickle, sqlite3 >>> def my_encode(obj): ... return sqlite3.Binary(zlib.compress(pickle.dumps(obj, pickle.HIGHEST_PROTOCOL))) >>> def my_decode(obj): ... return pickle.loads(zlib.decompress(bytes(obj))) >>> mydict = SqliteDict('./my_db.sqlite', encode=my_encode, decode=my_decode)
The module has no dependencies beyond Python itself.
Install or upgrade with:
pip install expiringsqlitedict
or from the source tar.gz:
python setup.py install
Standard Python document strings are inside the module:
>>> import expiringsqlitedict >>> help(expiringsqlitedict)
(but it’s just dict with a commit, really).
Beware: because of Python semantics, expiringsqlitedict cannot know when a mutable SqliteDict-backed entry was modified in RAM. For example, mydict.setdefault('new_key', ).append(1) will leave mydict['new_key'] equal to empty list, not . You’ll need to explicitly assign the mutated object back to SqliteDict to achieve the same effect:
>>> val = mydict.get('new_key', ) >>> val.append(1) # sqlite DB not updated here! >>> mydict['new_key'] = val # now updated
# pip install nose # pip install coverage
To perform all tests:
# make test-all
To perform all tests with coverage:
# make test-all-with-coverage
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